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Thread: Another Question on Prop Sizes

  1. #1

    Another Question on Prop Sizes

    Hey guys I've got a 5.1m Aquamaster Centre Console with a 90 etec running a stainless Viper 13 7/8 x 15 but due to carrying more and more weight with extra fuel and ice I'm struggling to reach even the lower end of the recommended rpm range for this motor (4100 rpm max on the weekend).

    Any suggestions on whether i get this prop reworked or on what size i should buy?

    Before anyone mentions it i have trialed a few solas props previously and found the viper was the best suited for the boat at the time but then again that may have all changed due to the extra weight??

    Cheers

  2. #2

    Re: Another Question on Prop Sizes

    I'm surprised it's struggling on is your motor set to the right height? I know it's a common question but is really a important one. If it is then going buy what you have stated you need to gain another 1000 rpm which would mean you would need to go down at least to a 12 pitch or even eleven.

    What year model is the etec.

    And what speed are you getting at that rpm.


    Sent from my iPhone using Ausfish mobile app
    560c Bar Crusher "Overtime"

  3. #3

    Re: Another Question on Prop Sizes

    That sounds more like a sick motor than an overweight boat.

  4. #4

    Re: Another Question on Prop Sizes

    I kinda agree as well that it sounds sick as my 90 pushes a 900kg boat with a 19p prop to 5400 revs.


    Sent from my iPhone using Ausfish mobile app
    560c Bar Crusher "Overtime"

  5. #5
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    Re: Another Question on Prop Sizes

    agree with others. i had a vengeance 16p on my 5.1m and could have gone to an 18p. that was only with a standard 75hp merc 2 stroke.

  6. #6

    Re: Another Question on Prop Sizes

    Yep. Something is not right. If you have the software and cable for the engine I would be running a cylinder drop test. You could try unloading the boat and running it as originally set up to see if you can achieve the required revs but if it's already sick this could potentially do more damage

  7. #7

    Re: Another Question on Prop Sizes

    Skusto it's an 08 model motor with approx 850 hrs and speed is 35-40km/hr which is about normal at 4000 rpm but it just didn't seem to have anything extra after that.

    I have noticed that when the boat is loaded for extended fishing/camping trips that it does struggle to reach max rpm but on a normal fishing trip without all the extra weight it seems to be fine. That's what made me think about changing the prop for these trips but I don't know to much about props.

    Just as a comparison a normal load would be 2 to 3 blokes, 110l of fuel and a 150l of esky with 20kg of ice, a few kg of bait and enough food and drinks for a day, where as the trip over the weekend was 2 blokes 270l of fuel, 330l of eskies with 80kg of ice, 14kg of bait plus enough food and drinks for 3 days and a fair bit of extra fishing gear thrown in on top.

    I do have a SST 14 3/4 x 17 prop sitting in the shed but that looks like a lot bigger one then the Viper.

  8. #8

    Another Question on Prop Sizes

    Ok your etec has the higher gear ratio to mine so that would explain mine being higher pitch.

    At a rough guide 1 degree pitch you get 200 rpm.

    The 90 optimum rev range is around 5000-5200

    The only problem going down like 3 pitches is your cruise and top speed will be reduced a fair bit.

    If you head over to the etec forum and search it will give you a heap of knowledge on the 90 etecs, that's were I have gained all the above from.

    Hope that helps.

    But it there could also be something wrong with the motor as well possibly.


    Sent from my iPhone using Ausfish mobile app
    560c Bar Crusher "Overtime"

  9. #9

    Re: Another Question on Prop Sizes

    Wow. Big RPM drop but that is a lot of weight for that size boat I suppose. General rule is an inch of pitch is good for 200 RPM meaning a 5 inch drop required to make 1000RPM. Don't think they make Vipers that low in pitch. I would be talking to Solas again or a similar prop professional as it may take a few goes to find something suitable. It would be worth trying the SST at least so you have more numbers for reference.

  10. #10

    Re: Another Question on Prop Sizes

    Thanks for the replies guys I might book it into Downes in the next week or so to get them to check it out just in case there is something a miss.

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